Although pulmonary transplantation has evolved into an effective therapy for end-stage lung disease, the balance between organ supply and demand greatly limits its applicability. Pulmonary xenotransplantation using swine lungs in humans could provide a solution to this problem. However, pulmonary xeno grafts develop rapidly are rejected by mechanisms distinct from those causing hyperacute rejection of the heart or kidney. The long-term objective of this project is to determine the mechanisms responsible for pulmonary xeno graft injury, develop strategies which will prevent this injury to enable the clinical application of pulmonary xenotransplantation. Although the mechanisms responsible for rejection of the cardiac xeno graft are dependent upon the binding of xeno reactive antibody to the Gal-a1,3-Gal epitope, the importance of this interaction in lung xeno grafts is unclear. The aims of this proposal are as follows: (1) define the role of xeno reactive antibody in pulmonary xeno graft injury; (2) to determine the significance of von Willebrand factor production and release from the pulmonary xeno graft on platelet activation in xeno reactive antibody function (3) to determine if C5a anaphylatoxin is the primary complement mediator of pulmonary xeno graft injury; and (4) to assess the resistance or susceptibility of the pulmonary xeno graft to acute vascular rejection and the possible relationship to xeno reactive antibody binding. The experiments outlined in this proposal will apply strategies for reducing xeno reactive antibody, reducing Gal-a1,3-Gal expression, eliminating von Willebrand factor production, blocking von Willebrand activity, and blocking C5a activity. In addition, techniques which prevent early xeno graft injury from occurring will be used to enable prolonged xeno graft function. It is anticipated that these studies will delineate the mechanisms responsible for early pulmonary xeno graft pulmonary xeno graft injury as well as aiding in the understanding of acute vascular rejection and possibly the development of accommodation. Strategies developed of these studies should allow the application of pulmonary xenotransplantation to the treatment of patients with pulmonary failure.